1. Field of the Invention
The present invention relates to a roller clutch built-in type pulley apparatus for an alternator to be used in an automobile.
A roller clutch built-in type pulley apparatus for an alternator to be provided by the present invention is fixed to an end portion of the rotary shaft of the alternator which serves as a power generator for a car for wrapping an endless belt onto a driving pulley fixed to an end portion of a crank shaft of the engine, so as to be utilized for driving the alternator. Particularly, the present invention is to realize a useful structure when using a so-called poly-V belt in which a plurality of projections each having a V-shaped cross section are extending along the entire circumference are provided on the inner peripheral surface thereof as the above-mentioned endless belt.
2. Related Background Art
The structure of an alternator for generating necessary electric power for a car by use of a driving engine of the car as its driving source is disclosed in, for example, Japanese Patent Laid-Open No.7-139550. FIG. 5 shows an alternator 1 disclosed in this application. In the alternator 1, a rotary shaft 3 is rotatably supported by a pair of rolling bearings 4, 4 inside the housing 2. In a middle part of this rotary shaft 3, there are provided a rotor 5 and a commutator 6. Also, a pulley 7 is fixed to a portion projecting outward from the housing 2 at one end (the right end in FIG. 5) of this rotary shaft 3. In a state in which it is assembled in the engine, an endless belt is passed over this pulley 7, so that the rotary shaft 3 is rotated and driven by means of a crank shaft of the engine.
As this pulley 7, hitherto a pulley which is simply fixed to the rotary shaft 3 is generally used. However, a variety of kinds of a roller clutch built-in type pulley apparatus for an alternator are proposed recently, which allows transmission of the power through the endless belt to the rotary shaft when a running speed of the endless belt is fixed or shows an upward trend, while allows a relative rotation between the pulley and the rotary shaft when the running speed of the endless belt shows downward trend. Some of such pulley apparatuses are used in practice. For example, a several kinds of such roller clutch built-in type pulley apparatus for an alternator having a function as mentioned above are disclosed in Japanese Patent Laid-Open Nos. 56-101353, 7-317807, 8-61443, and 8-226462, and Patent Publication No. 7-72585, French Patent Publication No. FR2726059A1, etc. Also, some of such roller clutch built-in type pulley apparatuses are actually used in practice.
Out of them, FIG. 6 shows the roller clutch built-in type pulley apparatus for an alternator disclosed in Japanese Patent Laid-Open No. 8-226462. This roller clutch built-in type pulley apparatus for an alternator has a sleeve 8 which is fitted on and fixed to the rotary shaft 3 of the alternator 1 (FIG. 5). Around this sleeve 8, a pulley 7a is provided concentrically with this sleeve 8. On the outer peripheral surface of this pulley 7a, there are formed a plurality of grooves 29, 29 each having V-shaped cross section and extending along the entire circumference in parallel to each other in the axial direction (the left and right direction in FIG. 6). An endless belt which is so-called a poly-V belt and which has a plurality of projections each having a V-shaped cross section and extending along the entire circumference on the inner peripheral surface of the belt is passed over such pulley 7a.
Then, a pair of support bearings 9, 9 and a roller clutch 10 are provided between the outer peripheral surface of the sleeve 8 and the inner peripheral surface of the pulley 7a. Out of them, the support bearings 9, 9 cause a relative rotation between the sleeve 8 and the pulley 7a, while supporting a radial load applied on the pulley 7a. On the other hand, the roller clutch 10 causes transmission of the rotating force from this pulley 7a to the sleeve 8 only when the pulley 7a is inclined to rotate relatively to the sleeve 8 in a given direction. In the structure shown In FIG. 6, the support bearings 9, 9 are cylindrical roller bearings. However, angular or deep groove ball bearings are conventionally known as being used as such support bearings, as disclosed, for example, in the above Japanese Patent Laid-Open No. 7-317807.
On the outer peripheral surface of the middle part of the inner race 24 which constitutes the roller clutch 10 and is fitted on and fixed to the sleeve 8, a plurality of recesses 25 called a ramp portion are formed at regular intervals in the circumferential direction, while a cam surface 26 is formed on the outer peripheral surface of the middle part. The outer peripheral surfaces of the both ends of the inner race 24 serve as inner race tracks 27, 27 for the support bearings 9, 9. On the other hand, the inner peripheral surface of the outer race 12 which constitutes the roller clutch 10 and is fitted on and fixed to the pulley 7a is simply formed as a cylindrical surface substantially over the entire length thereof. A plurality of rollers 11, 11 for constituting the roller clutch 10, together with the inner race 24 and the outer race 12, are supported by a retainer 28 to be capable of rolling and displacing a little in the circumferential direction. Then, there is provided a spring between a column portion arranged on this retainer 28 and each of the rollers 11 so that each of the rollers 11 is elastically pressed in the same direction with respect to the circumferential direction.
A roller clutch built-in type pulley apparatus for an alternator as mentioned above is used for the following reason. If, for example, the driving engine is a diesel engine, the angular velocity of rotation fluctuates largely when the engine is idling or rotated at low speed. As a result, the running speed of the unrepresented endless belt which is passed over the driving pulley fixed to the end of the crank shaft fluctuates minutely. On the other hand, the rotary shaft 3 of the alternator 1 which is driven to rotate by this endless belt through the pulley 7a does not fluctuate so drastically due to the inertial masses of this rotary shaft 3 and the rotor 5, the commutator 6 (FIG. 5), and the like fixed to this rotary shaft 3. Accordingly, when the pulley 7a is simply fixed with respect to the rotary shaft 3, the endless belt and the pulley 7a are inclined to rub against each other in the both directions upon fluctuation of the angular velocity of rotation of the crank shaft. As a result, the stress in different directions acts repeatedly on the endless belt which rubs against the pulley 7a, which causes easy slippery between this endless belt and the pulley 7a, or a shortened durability of the endless belt.
The shortened durability of the endless belt based on the friction between the outer peripheral surface of the pulley 7a and the inner peripheral surface of the endless belt as described above is also caused by repeated acceleration or deceleration at running time. That is, the driving force is transmitted from the endless belt side to the pulley 7a side at acceleration, while the braking force acts from the endless belt onto the pulley 7a which intends to continuously rotate based on inertia at deceleration, as described above. The braking force and the driving force respectively act as frictional forces in opposite directions for the inner peripheral surface of the endless belt, which also causes reduction in durability of the endless belt as a result. Particularly, in case of a vehicle equipped with an exhaust brake such as a motor truck, the rotation of the crank shaft when the accelerator is off is conspicuously decelerated, and the frictional force applied on the inner peripheral surface of the endless belt becomes large based on the above-mentioned braking force. As a result, the durability is conspicuously deteriorated.
Then, by the use the above-mentioned roller clutch built-in type pulley apparatus for an alternator as the pulley 7a, it is arranged such that the rotating force is transmitted from the pulley 7a to the rotary shaft 3 when the running speed of the endless belt is fixed or has an upward tendency, while the pulley 7a and the rotary shaft 3 are rotated relative to each other when the running speed of the endless belt has a downward tendency. That is, when the running speed of the endless belt has a downward tendency, the angular velocity of rotation of the pulley 7a is set lower than that of the rotary shaft 3, thereby preventing the endless belt and the pulley 7a from rubbing strongly against each other at a contact portion therebetween. With such arrangement, a direction of the stress which acts upon a part at which the pulley 7a and the endless belt rub against each other is fixed so as to prevent slippery between this endless belt and the pulley 7a or deterioration of the durability of the endless belt.
In order to design a pulley for rotating and driving the alternator 1, since conventionally it was primarily aimed to enhance the efficiency in the power generation by accelerating the rotation speed of the rotor 5, a space for installing the roller clutch 10 is reduced and the outer diameter D.sub.a of each of the rollers 11 for constituting this roller clutch 10 is also reduced. Consequently, in case of the conventionally-known roller clutch built-in type pulley apparatus for an alternator, a ratio D.sub.a /D.sub.o of the outer diameter D.sub.a of each of the rollers 11 to the inner diameter D.sub.o of the inner peripheral surface of the outer race 12, which constitutes the roller clutch 10 and is contacted by the rolling surface (the outer peripheral surface) of the roller 11, is about 0.05 to 0.07.
As described above, when a value for the ratio D.sub.a /D.sub.o of the outer diameter D.sub.a of each of the rollers 11 to the inner diameter D.sub.o of the inner peripheral surface of the outer race 12 is small, a load capacity of the roller clutch 10 becomes insufficient, so that a roller clutch built-in type pulley apparatus for an alternator having a sufficient durability can not be always realized. Particularly, the drawbacks mentioned above become conspicuous in the structure using the pulley 7a which has a plurality of grooves 29, 29 each having a V-shaped cross section and extending along the entire circumference formed on the outer peripheral surface thereof in parallel to each other in the axial direction, to carry the poly-V belt thereover, which is to be provided by the present invention. That is, in the structure using the poly-V belt as the endless belt, the outer diameter of this pulley 7a is often reduced to make the pulley apparatus light and compact, instead that a frictional area between the inner peripheral surface of the endless belt and the outer peripheral surface of the pulley 7a per unit length in the circumferential direction is enlarged. In case of such structure, the inner diameter D.sub.o of the inner peripheral surface of the outer race 12 becomes small so that a special consideration is required to securely maintain a necessary torque capacity.